New measuring equipment enhances research into electromechanical conversion

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DTU Energy has started research in electrostrictive, piezoelectric, dielectric and ferroelectric materials. New equipment makes the research easier and increases the possibility of teaching within the field.

Electromechanical conversion is a newly established research area at DTU Energy, which includes research in electrostrictive, piezoelectric, dielectric and ferroelectric materials. These are all materials that make up standard components in electrical actuators, sensors, transducers and capacitors.

As an example piezoelectric materials can generate very small amounts of electricity in the microwatt-milliwatt spectrum by being pulled or compressed, and through vibrations from both buildings and human movement. This makes piezoelectric materials extremely suitable for precise and fast measuring equipment as well as harvesting small amounts of energy for sensors inside the human body or other places where it is impractical to have and replace batteries.

“Piezoelectric materials are used for a wealth of acoustic devices, hearing aids, ultrasonic devices and as an example as acceleration sensors for airbags, where a sudden change in acceleration, like when a car drives into something and stops very quickly, cause the airbag to trigger," explains researcher Astri Bjørnetun Haugen, DTU Energy.

"DTU Energy researched in ceramic materials for decades and we have extensive knowledge of ceramics, but we haven’t had activities or special focus on these materials before now"

Astri Bjørnetun Haugen, researcher, DTU Energy

DTU Energy is cooperating with the company Meggitt A/S in Kvistgaard on an Industrial PhD project to find lead-free and environmentally friendly piezoelectric materials, and to facilitate this research project several new pieces of research equipment has been acquired with outside funding. The piezoelectric materials are not the only ones to enjoy the new equipment, as it allows the DTU researchers to explore new lead-free electrostritive materials as an alternative to the piezoelectric and ferroelectric materials for capacitors.

"DTU Energy researched in ceramic materials for decades and we have extensive knowledge of ceramics, but we haven’t had activities or special focus on these materials before now," says Astri Bjørnetun Haugen. She explains how DTU Energy has state-of-the-art facilities for ceramic processing but experienced a need for measurement and research equipment for the new materials.

The funding of the right equipment comes from among others Brødrene Hartmanns Fond, Siemens Fund and H.C. Ørsted's Fund, and their support has enabled DTU Energy to expand the research in the fields of electrostrictive, piezoelectric, dielectric and ferroelectric materials and opened for teaching and student projects in the fields as well.

"The foundations have helped us acquiring a small d33 meter and a larger ferroelectric characterization module (aixPES) that can supply high electrical voltage, and we are currently purchasing an important upgrade in the form of a laser interferometer," says Astri Bjørnetun Haugen.

With the aixPES module, the researchers are now able to study how the electrical polarization of a material develops when applied to an electric field. They are also able to see the characteristic hysteresis curves of ferroelectric materials.

Astri Bjørnetun Haugen explains how applying an electric field is necessary to make a material piezoelectric active and afterwards you can measure the piezoelectric coefficient d33. The process is simple as it is just a matter of placing the sample between two clips and applying pressure, the mechanical deformation creates electrical charges on the surfaces of the sample, and from the strength of these the material parameter d33 can be read directly from the d33 meter. The new equipment also makes it possible to measure the inverse piezoelectric effect - mechanical deformation under electric field at different conditions (temperature, electric field strength) with 0.3 nm resolution using the laser interferometer.

“This way the two new instruments complement each other and they can both easily and relatively quickly provide an overview of the piezoelectric properties of the selected material. They also make it possible to involve students in the research,” says Astri Bjørnetun Haugen explaining how successful student projects require that DTU Energy have equipment and facilities in place as the students have limited time.

“It takes time to coordinate and send samples for piezoelectric characterization to collaborators. We can do that ourselves now and in addition it motivates our students when they gain access to easy-to-use equipment and more so when their measurements can actually be used in the research."

The two newly acquired measuring instruments are very suitable for this purpose.

Electromechanical conversion

Materials that are able to change shape or volume when subjected to an electric field have important applications for actuators and sensors in many different contexts; and they can even be used for artificial muscles. However, most of the common materials for these purposes contain the toxic element lead. At DTU Energy we are researching new electromechanical materials that do not contain harmful elements. A particularly interesting group of materials are the so-called defective oxides, i.e. oxides that contain a large number of defects in the form of oxygen vacancies in their crystal lattices.

DTU Energy's main focus is functional metal oxides for the conversion of mechanical energy to electricity (and vice versa), but other applications are also possible. The new research is based on knowledge gained through decades of research in ceramic materials and manufacturing processes.

Currently, DTU Energy are mostly focusing on material development and manufacturing methods.

An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control signal and a source of energy. The control signal is relatively low energy and may be electric voltage or current, pneumatic or hydraulic pressure, or even human power. Its main energy source may be an electric current, hydraulic fluid pressure, or pneumatic pressure. When it receives a control signal, an actuator responds by converting the signal's energy into mechanical motion.

A capacitor is a passive two-terminal electrical component that stores potential energy in an electric field. The effect of a capacitor is known as capacitance. While some capacitance exists between any two electrical conductors in proximity in a circuit, a capacitor is a component designed to add capacitance to a circuit.

A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another

In the broadest definition, a sensor is a device, module, or subsystem whose purpose is to detect events or changes in its environment and send the information to other electronics, frequently a computer processor. A sensor is always used with other electronics, whether as simple as a light or as complex as a computer. Applications include manufacturing and machinery, airplanes and aerospace, cars, medicine, robotics and many other aspects of our day-to-day life.

At the Department of Energy Conversion and Storage we work on sustainable energy technologies. In the energy system of the future a large part of the energy will be supplied by fluctuating sources such as solar and wind power. This makes it critically important to be able to convert and store the energy as needed.